Amino acid utilization by Lactococcus lactis subsp cremoris FD1 during growth on yeast extract or casein peptone

Quantitative analyses of the utilization of amino acids by Lactococcus lactis subsp. cremoris FD1 in yeast extract medium (YE) and in casein peptone medium (CP) have been performed. Both free and peptide-bound amino acids were measured. In the CP most amino acids are peptide-bound and some amino acids are virtually only present in peptides. Thirty-six per cent of all peptide bonds in CP are hydrolysed during fermentation (6.3 mmol peptide bonds per gram biomass formed) and there is a transition of the growth rate related ATP consumption Y-xATP (mmol ATP g biomass(-1)) from 25 mmol g(-1) to 71 mmol g(-1) coincident with a decrease of the peptide consumption. In YE most of the amino acids are on the free form and only 26% of the peptide bonds are hydrolysed during fermentation (1.5 mmol peptide bonds per gram biomass formed). A constant Y-xATP = 38 mmol g(-1) prevails throughout the fermentation in YE.